Antimicrobial Peptides Grafted onto a Plasma Polymer Interlayer Platform: Performance upon Extended Bacterial Challenge

Modified polymeric biomaterials with antimicrobial and immunomodulating properties

The modification of the surgical polypropylene mesh and the polytetrafluoroethylene vascular prosthesis with cecropin A (small peptide) and puromycin (aminonucleoside) yielded very stable preparations of modified biomaterials. The main emphasis was placed on analyses of their antimicrobial activity and potential immunomodulatory and non-cytotoxic properties towards the CCD841 CoTr model cell line. Cecropin A did not significantly affect the viability or proliferation of the CCD 841 CoTr cells, regardless of its soluble or immobilized form. In contrast, puromycin did not induce a significant decrease in the cell viability or proliferation in the immobilized form but significantly decreased cell viability and proliferation when administered in the soluble form. The covalent immobilization of these two molecules on the surface of biomaterials resulted in stable preparations that were able to inhibit the multiplication of Staphylococcus aureus and S. epidermidis strains. It was also found that the preparations induced the production of cytokines involved in antibacterial protection mechanisms and stimulated the immune response. The key regulator of this activity may be related to TLR4, a receptor recognizing bacterial LPS. In the present study, these factors were produced not only in the conditions of LPS stimulation but also in the absence of LPS, which indicates that cecropin A- and puromycin-modified biomaterials may upregulate pathways leading to humoral antibacterial immune response.

A comprehensive status update on modification of foley catheter to combat catheter-associated urinary tract infections and microbial biofilms

Present-day healthcare employs several types of invasive devices, including urinary catheters, to improve medical wellness, the clinical outcome of disease, and the quality of patient life. Among urinary catheters, the Foley catheter is most commonly used in patients for bladder drainage and collection of urine. Although such devices are very useful for patients who cannot empty their bladder for various reasons, they also expose patients to catheter-associated urinary tract infections (CAUTIs). Catheter provides an ideal surface for bacterial colonization and biofilm formation, resulting in persistent bacterial infection and severe complications. Hence, rigorous efforts have been made to develop catheters that harbour antimicrobial and anti-fouling properties to resist colonization by bacterial pathogens. In this regard, catheter modification by surface functionalization, impregnation, blending, or coating with antibiotics, bioactive compounds, and nanoformulations have proved to be effective in controlling biofilm formation. This review attempts to illustrate the complications associated with indwelling Foley catheters, primarily focussing on challenges in fighting CAUTI, catheter colonization, and biofilm formation. In this review, we also collate scientific literature on catheter modification using antibiotics, plant bioactive components, bacteriophages, nanoparticles, and studies demonstrating their efficacy through in vitro and in vivo testing.

Staphylococcus aureus surface attachment selectively influences tolerance against charged antibiotics

The threat of infection during implant placement surgery remains a considerable burden for millions of patients worldwide. To combat this threat, clinicians employ a range of anti-infective strategies and practices. One of the most common interventions is the use of prophylactic antibiotic treatment during implant placement surgery. However, these practices can be detrimental by promoting the resilience of biofilm-forming bacteria and enabling them to persist throughout treatment and re-emerge later, causing a life-threatening infection. Thus, it is of the utmost importance to elucidate the events occurring during the initial stages of bacterial surface attachment and determine whether any biological processes may be targeted to improve surgical outcomes. Using gene expression analysis, we identified a cellular mechanism of S. aureus which modifies its cell surface charge following attachment to a medical grade titanium surface. We determined the upregulation of two systems involved in the d-alanylation of teichoic acids and the lysylation of phosphatidylglycerol. We supported these molecular findings by utilizing synchrotron-sourced attenuated total reflection Fourier-transform infrared microspectroscopy to analyze the biomolecular properties of the S. aureus cell surface following attachment. As a direct consequence, S. aureus quickly becomes substantially more tolerant to the positively charged vancomycin, but not the negatively charged cefazolin. The present study can assist clinicians in rationally selecting the most potent antibiotic in prophylaxis treatments. Furthermore, it highlights a cellular process that could potentially be targeted by novel technologies and strategies to improve the outcome of antibiotic prophylaxis during implant placement surgery. STATEMENT OF SIGNIFICANCE: The antibiotic tolerance of bacteria in biofilm is a well-established phenomenon. However, the physiological adaptations employed by Staphylococcus aureus to increase its antibiotic tolerance during the early stages of surface attachment are poorly understood. Using multiple techniques, including gene expression analysis and synchrotron-sourced Fourier-transform infrared microspectroscopy, we generated insights into the physiological response of S. aureus following attachment to a medical grade titanium surface. We showed that this phenotypic transition enables S. aureus to better tolerate the positively charged vancomycin, but not the negatively charged cefazolin. These findings shed light on the antibiotic tolerance mechanisms employed by S. aureus to survive prophylactically administered antibiotics and can help clinicians to protect patients from infections.

From Basics to Frontiers: A Comprehensive Review of Plasma-Modified and Plasma-Synthesized Polymer Films

This comprehensive review begins by tracing the historical development and progress of cold plasma technology as an innovative approach to polymer engineering. The study emphasizes the versatility of cold plasma derived from a variety of sources including low-pressure glow discharges (e.g., radiofrequency capacitively coupled plasmas) and atmospheric pressure plasmas (e.g., dielectric barrier devices, piezoelectric plasmas). It critically examines key operational parameters such as reduced electric field, pressure, discharge type, gas type and flow rate, substrate temperature, gap, and how these variables affect the properties of the synthesized or modified polymers. This review also discusses the application of cold plasma in polymer surface modification, underscoring how changes in surface properties (e.g., wettability, adhesion, biocompatibility) can be achieved by controlling various surface processes (etching, roughening, crosslinking, functionalization, crystallinity). A detailed examination of Plasma-Enhanced Chemical Vapor Deposition (PECVD) reveals its efficacy in producing thin polymeric films from an array of precursors. Yasuda's models, Rapid Step-Growth Polymerization (RSGP) and Competitive Ablation Polymerization (CAP), are explained as fundamental mechanisms underpinning plasma-assisted deposition and polymerization processes. Then, the wide array of applications of cold plasma technology is explored, from the biomedical field, where it is used in creating smart drug delivery systems and biodegradable polymer implants, to its role in enhancing the performance of membrane-based filtration systems crucial for water purification, gas separation, and energy production. It investigates the potential for improving the properties of bioplastics and the exciting prospects for developing self-healing materials using this technology.

Effect of Quorum Sensing Molecule Farnesol on Mixed Biofilms of Candida albicans and Staphylococcus aureus

The natural bioactive molecule farnesol (FAR) is widely studied mainly for its antibiofilm and antimicrobial properties. In addition, it increases the effectiveness of some antimicrobial substances, which makes it interesting for the development of combined therapy. In the present work, the effect of FAR either alone or in combination with oxacillin (OXA) on mixed biofilms formed by clinically relevant pathogens, Candida albicans and Staphylococcus aureus, was studied. S. aureus isolates used for biofilm formation originated from blood cultures and central venous catheters (CVC) were characterized in terms of antimicrobial resistance. The minimal biofilm inhibitory concentration (MBIC50) for FAR of 48 h mixed biofilms formed by the C. albicans and methicillin-sensitive S. aureus (MSSA) was determined to be 125 μM, and for the mixed biofilms with methicillin-resistant S. aureus (MRSA) was determined to be 250 μM. Treatment of mixed biofilms with OXA (2 mg/mL) showed ≤4% inhibition; however, the combination of OXA (2 mg/mL) and FAR (300 μM) resulted in 80% inhibition of biofilms. In addition, planktonic cells of S. aureus exhibited an increased susceptibility to OXA, cefoxitin and kanamycin in the presence of FAR (150 and 300 μM). Scanning electron microscopy (SEM) micrographs confirmed patchy biofilm and lack of candidal hyphae in the samples treated with FAR and FAR/OXA in comparison to control and mixed biofilms treated only with OXA. Intriguingly, in a pilot experiment using fluorescence in situ hybridization (FISH), considerable differences in activity (as indicated by ribosome content) of staphylococcal cells were detected. While the activity rate of the staphylococci in mixed biofilms treated with FAR was high, no FISH-positive signal for staphylococcal cells was found in the biofilm treated with FAR/OXA.

Substrate-independent and widely applicable deposition of antibacterial coatings

Antibacterial coatings are regarded as a necessary tool to prevent implant-related infections. Substrate-independent and widely applicable coating techniques are gaining significant interest to synthesize different types of antibacterial films, which can be relevant from a fundamental and application-oriented perspective. Plasma polymer- and polydopamine-based antibacterial coatings represent the most widely studied and versatile approaches among these coating techniques. Both single- and dual-functional antibacterial coatings can be fabricated with these approaches and a variety of dual-functional antibacterial coating strategies can still be explored in future work. These coatings can potentially be used for a wide range of different implants (material, shape, and size). However, for most implants, significantly more fundamental knowledge needs to be gained before these coatings can find real-life use.

Bio-Inspired Nanostructured Ti-6Al-4V Alloy: The Role of Two Alkaline Etchants and the Hydrothermal Processing Duration on Antibacterial Activity

Inspired by observations that the natural topography observed on cicada and dragonfly wings may be lethal to bacteria, researchers have sought to reproduce these nanostructures on biomaterials with the goal of reducing implant-associated infections. Titanium and its alloys are widely employed biomaterials with excellent properties but are susceptible to bacterial colonisation. Hydrothermal etching is a simple, cost-effective procedure which fabricates nanoscale protrusions of various dimensions upon titanium, depending on the etching parameters used. We investigated the role of etching time and the choice of cation (sodium and potassium) in the alkaline heat treatment on the topographical, physical, and bactericidal properties of the resulting modified titanium surfaces. Optimal etching times were 4 h for sodium hydroxide (NaOH) and 5 h for potassium hydroxide (KOH). NaOH etching for 4 h produced dense, but somewhat ordered, surface nanofeatures with 75 nanospikes per µm². In comparison, KOH etching for 5 h resulted sparser but nonetheless disordered surface morphology with only 8 spikes per µm². The NaOH surface was more effective at eliminating Gram-negative pathogens, while the KOH surface was more effective against the Gram-positive strains. These findings may guide further research and development of bactericidal titanium surfaces which are optimised for the predominant pathogens associated with the intended application.

Antibacterial Activity of Rose Bengal Entrapped in Organically Modified Silica Matrices

Photosensitizers (PSs) are known as powerful antibacterial agents that are activated by direct exposure to visible light. PSs can be noncovalently entrapped into the silica gel network for their controlled release into a contaminated area. The immobilization of PS-containing gel matrices on a polymer support expands their possible applications, such as antibacterial surfaces and coatings, which can be used for the disinfection of liquids. In the current study, we report the use of Rose Bengal (RB) incorporated into organically modified silica matrices (RB@ORMOSIL matrices) by the sol-gel technique. The RB matrices exhibit high activity against Gram-positive and Gram-negative bacteria under illumination by white light. The amount and timing of solidifier addition to the matrix affected the interaction of the latter with the RB, which in turn could affect the antibacterial activity of RB. The most active specimen against both Gram-positive and Gram-negative bacterial cells was the RB6@ORMOSIL matrix immobilized on a linear low-density polyethylene surface, which was prepared by an easy, cost-effective, and simple thermal adhesion method. This specimen, RB6@OR@LLDPE, showed the low release of RB in an aqueous environment, and exhibited high long-term antibacterial activity in at least 14 rounds of recycled use against S. aureus and in 11 rounds against E. coli.

Long-term antibacterial properties of a nanostructured titanium alloy surface: An in vitro study

The demand for joint replacement and other orthopedic surgeries involving titanium implants is continuously increasing; however, 1%-2% of surgeries result in costly and devastating implant associated infections (IAIs). Pseudomonas aeruginosa and Staphylococcus aureus are two common pathogens known to colonise implants, leading to serious complications. Bioinspired surfaces with spike-like nanotopography have previously been shown to kill bacteria upon contact; however, the longer-term potential of such surfaces to prevent or delay biofilm formation is unclear. Hence, we monitored biofilm formation on control and nanostructured titanium disc surfaces over 21 days following inoculation with Pseudomonas aeruginosa and Staphylococcus aureus. We found a consistent 2-log or higher reduction in live bacteria throughout the time course for both bacteria. The biovolume on nanostructured discs was also significantly lower than control discs at all time points for both bacteria. Analysis of the biovolume revealed that for the nanostructured surface, bacteria was killed not just on the surface, but at locations above the surface. Interestingly, pockets of bacterial regrowth on top of the biomass occurred in both bacterial species, however this was more pronounced for S. aureus cultures after 21 days. We found that the nanostructured surface showed antibacterial properties throughout this longitudinal study. To our knowledge this is the first in vitro study to show reduction in the viability of bacterial colonisation on a nanostructured surface over a clinically relevant time frame, providing potential to reduce the likelihood of implant associated infections.

Plasma surface modification strategies for the preparation of antibacterial biomaterials: A review of the recent literature

Plasma-based strategies offer several advantages for developing antibacterial biomaterials and can be used directly or combined with other surface modification techniques. Direct plasma strategies can be classified as plasma surface modifications that derive antibacterial property by tailoring surface topography or surface chemistry. Nano patterns induced by plasma modification can exhibit antibacterial property and promote the adhesion and proliferation of mammalian cells, creating antibacterial and biocompatible surfaces. Antibacterial effect by tailoring surface chemistry via plasma can be attained by either creating bacteriostatic surfaces or bactericidal surfaces. Plasma-assisted strategies incorporate plasma processes in combination with other surface modification techniques. Plasma coating can serve as a drug-eluting reservoir and diffusion barrier. The plasma-functionalized surface can serve as a platform for grafting antibacterial agents, and plasma surface activation can improve the adhesion of polymeric layers with antibacterial properties. This article critically reviews plasma-based strategies reported in the recent literature for the development of antibacterial biomaterial surfaces. Studies using both atmospheric and low-pressure plasmas are included in this review. The findings are discussed in terms of the trends in material and precursor selection, modification stability, antibacterial efficacy, the choice of bacterial strains tested, cell culture findings, critical aspects of in vitro performance testing and in vivo experimental design.

Decontamination-Induced Modification of Bioactivity in Essential Oil-Based Plasma Polymer Coatings

Plasma polymer coatings fabricated from Melaleuca alternifolia essential oil and its derivatives have been previously shown to reduce the extent of microbial adhesion on titanium, polymers, and other implantable materials used in dentistry. Previous studies have shown these coatings to maintain their performance under standard operating conditions; however, when used in e.g., a dental implant, these coatings may inadvertently become subject to in situ cleaning treatments, such as those using an atmospheric pressure plasma jet, a promising tool for the effective in situ removal of biofilms from tissues and implant surfaces. Here, we investigated the effect of such an exposure on the antimicrobial performance of the Melaleuca alternifolia polymer coating. It was found that direct exposure of the polymer coating surface to the jet for periods less than 60 s was sufficient to induce changes in its surface chemistry and topography, affecting its ability to retard subsequent microbial attachment. The exact effect of the jet exposure depended on the chemistry of the polymer coating, the length of plasma treatment, cell type, and incubation conditions. The change in the antimicrobial activity for polymer coatings fabricated at powers of 20–30 W was not statistically significant due to their limited baseline bioactivity. Interestingly, the bioactivity of polymer coatings fabricated at 10 and 15 W against Staphylococcus aureus cells was temporarily improved after the treatment, which could be attributed to the generation of loosely attached bioactive fragments on the treated surface, resulting in an increase in the dose of the bioactive agents being eluted by the surface. Attachment and proliferation of Pseudomonas aeruginosa cells and mixed cultures were less affected by changes in the bioactivity profile of the surface. The sensitivity of the cells to the change imparted by the jet treatment was also found to be dependent on their origin culture, with mature biofilm-derived P. aeruginosa bacterial cells showing a greater ability to colonize the surface when compared to its planktonic broth-grown counterpart. The presence of plasma-generated reactive oxygen and nitrogen species in the culture media was also found to enhance the bioactivity of polymer coatings fabricated at power levels of 10 and 15 W, due to a synergistic effect arising from simultaneous exposure of cells to reactive oxygen and nitrogen species (RONS) and eluted bioactive fragments. These results suggest that it is important to consider the possible implications of inadvertent changes in the properties and performance of plasma polymer coatings as a result of exposure to in situ decontamination, to both prevent suboptimal performance and to exploit possible synergies that may arise for some polymer coating-surface treatment combinations.

Impact of Healthcare-Associated Infections Connected to Medical Devices-An Update

Healthcare-associated infections (HAIs) are caused by nosocomial pathogens. HAIs have an immense impact not only on developing countries but also on highly developed parts of world. They are predominantly device-associated infections that are caused by the planktonic form of microorganisms as well as those organized in biofilms. This review elucidates the impact of HAIs, focusing on device-associated infections such as central line-associated bloodstream infection including catheter infection, catheter-associated urinary tract infection, ventilator-associated pneumonia, and surgical site infections. The most relevant microorganisms are mentioned in terms of their frequency of infection on medical devices. Standard care bundles, conventional therapy, and novel approaches against device-associated infections are briefly mentioned as well. This review concisely summarizes relevant and up-to-date information on HAIs and HAI-associated microorganisms and also provides a description of several useful approaches for tackling HAIs.

Comparative Study of Natural Terpenoid Precursors in Reactive Plasmas for Thin Film Deposition

If plasma polymer thin films are to be synthesised from sustainable and natural precursors of chemically heterogeneous composition, it is important to understand the extent to which this composition influences the mechanism of polymerisation. To this end, a well-studied monoterpene alcohol, terpinen-4-ol, has been targeted for a comparative study with the naturally occurring mix of terpenes (viz. Melaleuca alternifolia oil) from which it is commonly distilled. Positive ion mode mass spectra of both terpinen-4-ol and M. alternifolia oil showed a decrease in disparities between the type and abundance of cationic species formed in their respective plasma environments as applied plasma power was increased. Supplementary biological assay revealed the antibacterial action of both terpinen-4-ol and M. alternifolia derived coatings with respect to S. aureus bacteria, whilst cytocompatibility was demonstrated by comparable eukaryotic cell adhesion to both coatings. Elucidating the processes occurring within the reactive plasmas can enhance the economics of plasma polymer deposition by permitting use of the minimum power, time and precursor pre-processing required to control the extent of monomer fragmentation and fabricate a film of the desired thickness and functionality.